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ORIGINAL ARTICLE
Year : 2010  |  Volume : 56  |  Issue : 3  |  Page : 182-185

Detection of inducible clindamycin resistance among Staphylococcal isolates from different clinical specimens in western India


Department of Microbiology, SMS Medical College, Jaipur, India

Date of Submission26-Jul-2009
Date of Decision22-Apr-2010
Date of Acceptance17-May-2010
Date of Web Publication23-Aug-2010

Correspondence Address:
N Pal
Department of Microbiology, SMS Medical College, Jaipur
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0022-3859.68637

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 :: Abstract 

Background: Macrolide (MLS B ) resistance is the most widespread and clinically important mechanism of resistance encountered with Gram-positive organisms. Resistance may be constitutive (cMLS B phenotype) or inducible (iMLS B phenotype). The iMLS B phenotypes are not differentiated by using standard susceptibility test methods, but can be distinguished by erythromycin-clindamycin disk approximation test (D-test) and demonstration of resistance genes by molecular methods. Aims: To demonstrate in vitro inducible clindamycin resistance (iMLS B ) in erythromycin-resistant (ER) and clindamycin-susceptible (CLI-S) clinical isolates of Staphylococci spp., and interpretation of susceptibility tests to guide therapy. Materials and Methods: Eight hundred and fifty-one isolates of Staphylococci spp. were recovered from various clinical specimens. All the Staphylococcal spp. were identified by conventional microbiological methods including colony morphology, Gram stain, catalase, slide coagulase and tube coagulase. Antibiotic susceptibility testing was performed by Kirby Bauer disc diffusion method. Erythromycin-resistant isolates were examined for inducible clindamycin resistance (iMLS B ) by using double disk approximation test (D-test) at 15 mm disk separation. Results: The Staphylococci spp. isolated were 379 S. aureus [31.60% methicillin-resistant S. aureus (MRSA), 12.92% methicillin-sensitive S. aureus (MSSA)] and 472 coagulase-negative Staphylococci (CNS) [37.60% methicillin-resistant coagulase-negative Staphylococci (MRCNS), 17.86% methicillin-sensitive coagulase-negative Staphylococci (MSCNS)]. Four hundred and thirty (50.52%) Staphylococcal spp. isolates showed erythromycin resistance. Constitutive resistance was demonstrated in 202 (46.97%), inducible clindamycin resistance (iMLS B ) in 101 (23.48%), and non-inducible (MS) in 127 (29.53%). Two distinct induction phenotypes, D (18.13%) and D + (5.34%) were observed. All iMLS B isolates were susceptible to linezolid and vancomycin while 78.78% to ciprofloxacin. Conclusions: Fifty percent of Staphylococcal spp. were ER among which 23.48% were iMLS B phenotypes. Eighty-seven per cent of iMLS B phenotypes were observed to be methicillin-resistant. The high frequency of methicillin resistance isolates (87.12%) with in vitro inducible clindamycin resistance at our institute raises concern of clindamycin treatment failures with methicillin-resistant infections. So we recommend that microbiology laboratories should include the D-test for inducible resistance to clindamycin in the routine antibiotic susceptibility testing.


Keywords: D-test, inducible clindamycin resistance, Staphylococcus aureus


How to cite this article:
Pal N, Sharma B, Sharma R, Vyas L. Detection of inducible clindamycin resistance among Staphylococcal isolates from different clinical specimens in western India. J Postgrad Med 2010;56:182-5

How to cite this URL:
Pal N, Sharma B, Sharma R, Vyas L. Detection of inducible clindamycin resistance among Staphylococcal isolates from different clinical specimens in western India. J Postgrad Med [serial online] 2010 [cited 2019 Mar 26];56:182-5. Available from: http://www.jpgmonline.com/text.asp?2010/56/3/182/68637



 :: Introduction Top


Staphylococcus aureus and coagulase-negative Staphylococci (CNS) infections have become common among both hospitalized and non-hospitalized patients. The emergence of resistance to antimicrobial agents among Staphylococci is an increasing problem.

The development of resistance in Staphylococcus species to macrolide, lincosamide and streptogramin B has limited the use of these antibiotics. Macrolide resistance may be due to enzymes encoded by a variety of erm genes-MLS B phenotype and may be constitutive (cMLS B phenotype) or inducible (iMLS B phenotype). Another mechanism is active efflux pump encoded by the mrs A gene (MS phenotype). The MS and iMLS B phenotypes are indistinguishable by using standard susceptibility test methods, but can be distinguished by erythromycin-clindamycin disk approximation test (D-test) and demonstration of resistance genes by molecular methods. [1],[2]

The aim of this study was to determine the rate of inducible clindamycin resistance in both methicillin-resistant and susceptible strains of Staphylococcus in our hospital as data describing iMLS B prevalence among Staphylococcus isolates in this region is unknown.


 :: Materials and Methods Top


Eight hundred and fifty-one isolates of Staphylococci spp. were recovered from blood, cerebrospinal fluid, pus, sputum, tracheal aspirate, nasal swab, urine and other specimens received in the Department of Microbiology over a period of nine months from August 2008 to April 2009.

All the Staphylococcal species were identified by conventional microbiological methods including colony morphology, gram stain, catalase, slide coagulase and tube coagulase test.

Antibiotic susceptibility testing was performed by Kirby Bauer disc diffusion method. Antibiotic discs used were ampicillin (10 μg), amoxiclav (20/10 μg), cefepime (30 μg), ceftriaxone (30 μg), cephotaxime (30 μg), cefoperazone-sulbactam (75/30 μg), cephalexin (30 μg), ciprofloxacin (5 μg),) doxycycline (30 μg), erythromycin (15 μg), linezolid (30 μg), netilmicin (30 μg), piperacillin-tazobactum (100/10μg) and vancomycin (30μg).

Methicillin resistance was detected by agar screen test. Inoculum was prepared by suspending organisms from 24-h culture in sterile saline and adjusting the turbidity to 0.5 McFarland. A sterile cotton swab was dipped into the bacterial suspension; spot inoculated on Mueller-Hinton agar plate (supplemented with 4% NaCl containing 6 μg of oxacillin per ml). The plates were incubated at 35 0 C for 24 h for Staphylocccus aureus and 48 h for coagulase-negative Staphyloccci (CNS). Growth of even a single colony is indicative of resistance. [3]

Disk approximation testing (D-test) was performed for each isolate according to Clinical and Laboratory Standards Institute (CLSI) method. [4] A 0.5 McFarland suspension was prepared in normal saline for each isolate and inoculated on Mueller-Hinton agar plate. Clindamycin (CLI)-2 μg and erythromycin (ER)-15μg disks were placed 15 mm apart edge to edge manually. Plates were incubated at 35 0 C for 24 h and zone diameters were recorded. Induction test categories were interpreted as given in [Table 1]. [2]
Table 1: Characteristics of clindamycin induction test phenotypes as tested by disk approximation test

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 :: Results Top


A total of 851 Staphylococcal spp. isolates were included, of which 379 were S. aureus [31.60% methicillin-resistant S. aureus (MRSA), 12.92% methicillin-sensitive S. aureus (MSSA)] and 472 CNS [37.60% methicillin-resistant CNS (MRCNS), 17.86% methicillin-sensitive CNS (MSCNS)]. Categorization of the isolates along with sources is depicted in [Table 2].
Table 2: Sources and categorization of Staphylococcal isolates

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Four hundred and thirty (50.52%) clinical isolates which showed erythromycin resistance were tested for inducible resistance by double disk approximation test. Out of 430 erythromycin-resistant strains 101 (23.48%) were iMLS B phenotypes [43.56% MRSA (44/101), 6.93% MSSA (7/101), 43.56% (44/101) MRCNS and 6.0% (6/101) MSCNS].

Eighty-eight (87.12%) iMLS B phenotypes were observed to be methicillin-resistant.

D-test yielded two distinct induction phenotypes, D-zone phenotype [Figure 1] was observed in 78 (18.13%) and D + phenotype [Figure 2] in 22 (5.34%) isolates. Both D and D + results were considered positive for CLI induction- iMLS B phenotypes. One hundred and twenty-seven (29.53%) isolates showed ERresistant and CLI-susceptible zone diameters with no blunting of the zones (MS phenotype). Two hundred and two (46.97%) isolates showed ER and CLI resistance (cMLS B phenotype), of which 98 were MRCNS, 85 MRSA and the rest were methicillin-sensitive [Table 3]. No hazy D zone (HD) phenotype was observed.
Table 3: MLSB resistance phenotypes in S. aureus and CNS isolates

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Figure 1: Inducible MLSB isolate- D phenotype

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Figure 2: Inducible MLSB isolate- D+ phenotype

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Susceptibility of iMLS B phenotypes isolated were ampicillin 37.5%, amoxiclav 39.13%, cefepime 12.5%, ceftriaxone 50.0%, cephotaxime 62.5%, cefoperazone-sulbactam 60.86%, cephalexin 23.07%, ciprofloxacin 78.78%, doxycycline 69.56%, linezolid 100%, netilmicin 46.60%, piperacillin-tazobactum 69.56% and vancomycin 100%.


 :: Discussion Top


In our study, 851 Staphyloccocal isolates were obtained over a period of nine months (2008-09) in which 50.52% were ER-resistant. Among the ER-resistant S. aureus iMLS B resistance was observed in 24.63% (51/207) similar to that reported by Gadepalli et al., Fiebelkorn et al., and Jorgensen et al. [5],[6],[7] Some investigators have reported a higher incidence [8],[9],[10],[11],[12],[13] (iMLS B resistance) while others have indicated lower incidence. [14],[15],[16],[17],[18] We observed almost a similar rate of iMLS B resistance among S. aureus (24.63%) and CNS (22.42%), while others have reported variable results. The different patterns of resistance observed in various studies are because iMLS B resistance varies by geographical region, age group, methicillin susceptibility and even from hospital to hospital.

As observed in studies by Steward et al., and Schreckenberger et al., our CLI induction results also showed two phenotypes, D (18.13%) and D + (5.34%) phenotypes and both are considered to be positive D-zone test. [2],[19]

All our iMLS B isolates were susceptible to linezolid and vancomycin while 78.78% to ciprofloxacin. Rahbar and Hajia also found all iMLS B isolates susceptible to linezolid and vancomycin. [14]

Due to the emergence of resistance to antimicrobial agents accurate drug susceptibility data of the infecting microbe is an essential factor in making appropriate therapeutic decisions. MLS B resistance is the most widespread and clinically important mechanism of resistance encountered with Gram-positive organisms due to the production of methylases and efflux proteins. In vitro susceptibility testing for clindamycin may indicate false susceptibility by the broth microdilution method and by disk diffusion testing with erythromycin and clindamycin disks in nonadjacent positions. Erythromycin-clindamycin disc approximation test or D-test is a simple, reliable method to detect inducible resistance to clindamycin in erythromycin-resistant isolates of Staphylococci. [2, 6, 14] Sensitivity of D-test performed at 15-20 mm disk spacing was 100% when correlated with detection of erm and msr genes by polymerase chain reaction(PCR). [2],[6],[7],[9],[10]

Clinically, bacterial strains exhibiting iMLS B have a high rate of spontaneous mutation to constitutive resistance and use of non-inducer antibiotics such as clindamycin can lead to selection of constitutive mutants at frequencies of 10 -7 cfu. [8],[9],[19],[20] McGehee and other investigators have confirmed this rapid in vitro conversion of inducible to constitutive MLS B resistance in Staphylococci. [20],[21] There have also been a number of reported clindamycin or lincomycin therapy failures in serious infections due to Staphylococci with iMLS B resistance, indicating that it is not uncommon. [1],[20] Clindamycin has long been an attractive option in the treatment of skin and soft tissue infections (SSTI) and serious infections because of its efficacy against MRSA and MSSA, as well as anaerobes. This has led to questioning the efficacy of clindamycin use against any erythromycin-resistant Staphylococci spp. However, if inducible resistance can be reliably detected on a routine basis in clinically significant isolates, clindamycin can be safely and effectively used in patients with true clindamycin-susceptible strains.

In the present study, 29.53% of erythromycin-resistant Staphylococcal isolates showed true clindamycin susceptibility (MS phenotype). Patients with infections caused by such isolates can be treated with clindamycin without emergence of resistance during therapy.

The high frequency of methicillin-resistance isolates (87.12%) with in vitro inducible clindamycin resistance at our institute raises concern of clindamycin treatment failures with methicillin-resistant infections.

We conclude that it is important for laboratories to be aware of the local prevalence of iMLS B isolates. On the basis of their data they can choose whether or not to perform the D-test routinely. The D-test is an easy, sensitive, and reliable means for detection of iMLS B strains in a clinical laboratory setting without specialized testing facilities. [9] This prevalence of iMLS B may change over time with the emergence of strains with different sensitivity patterns, so periodic surveys should be performed if testing is not routine.

 
 :: References Top

1.Drinkovic D, Fuller ER, Shore KP, Holland DJ, Rod Ellis Pegler. Clindamycin treatment of Staphylococcus aureus expressing inducible clindamycin resistance. J Antimicrob Chemother 2001;48:315-6.  Back to cited text no. 1      
2.Steward CD, Raney PM, Morrell AK, Williams PP, McDougal LK, Jevitt L, et al. Testing for induction of clindamycin resistance in erythromycin-resistant isolates of Staphylococcus aureus. J Clin Microbiol 2005;43:1716-21.  Back to cited text no. 2  [PUBMED]  [FULLTEXT]  
3.Corinne JH, Henry FC. Methicillin-resistant staphylococci: Detection methods and treatment of infections. Antimicrob Agents Chemother 1989;33:995-9.  Back to cited text no. 3      
4.Clinical and Laboratory Standards Institute (CLSI). Performance Standards for Antimicrobial disk susceptibility Tests: Approved Standard M2-A7. 11 th ed. Clinical and Laboratory Standards Institute Wayne, Pa; 2005.  Back to cited text no. 4      
5.Gadepalli R, Dhawan B, Mohanty S, Kapil A, Das BK, Chaudhry R. Inducible clindamycin resistance in clinical isolates of Staphylococcus aureus. Indian J Med Res 2006;123:571-3.   Back to cited text no. 5  [PUBMED]  [FULLTEXT]  
6.Fiebelkorn KR, Crawford SA, McElmeel ML, Jorgensen JH. Practical disk diffusion method for detection of inducible clindamycin resistance in Staphylococcus aureus and coagulase-negative staphylococci. J Clin Microbiol 2003;41:4740-4.  Back to cited text no. 6  [PUBMED]  [FULLTEXT]  
7.Jorgensen JH, Crawford SA, McElmeel MLand Fiebelkorn KR. Detection of inducible clindamycin resistance of Staphylococci in conjunction with performance of automated broth susceptibility testing. J Clin Microbiol 2004;42:1800-2.  Back to cited text no. 7      
8.Goyal R, Singh NP, Manchanda V, Mathur M. Detection of clindamycin susceptibility in macrolides resistant phenotypes of Staphylococcus aureus. Indian J Med Microbiol 2004;22:251-4.  Back to cited text no. 8  [PUBMED]  Medknow Journal  
9.O'Sullivan MV, Cai Y, Kong F, Zeng X, Gilbert GL. The influence of disk separation distance on the accuracy of the disk approximation testing for inducible clindamycin resistance in Staphylococcus spp. J Clin Microbiol 2006;44:4072-6.  Back to cited text no. 9  [PUBMED]  [FULLTEXT]  
10.Merino L, Torres MJ, Cantos A, Ruiz M, Aznar J. Detection of inducible clindamycin resistance in cutaneous Staphylococci clinical isolates by phenotypic and genotypic method. Abstract number: 1134_02_427.15 th European Congress of Clinical Microbiology and Infectious Diseases Copenhagen / Denmark, April 2-5, 2005.  Back to cited text no. 10      
11.Angel MR, Balaji V, Prakash J, Brahmadathan KN, Mathews MS. Prevalence of inducible clindamycin resistance in gram positive organisms in a tertiary care centre. Indian J Med Microbiol 2008;26:262-4.  Back to cited text no. 11  [PUBMED]  Medknow Journal  
12.Ciraj AM, Vinod P, Sreejith G, Rajani K. Inducible clindamycin resistance among clinical isolates of staphylococci. Indian J Pathol Microbiol 2009;52:49-51.  Back to cited text no. 12  [PUBMED]  Medknow Journal  
13.Patel M, Waites KB, Moser SA, Cloud GA, Hoesley CJ. Prevalence of inducible clindamycin resistance among community and hospital-associated Staphylococcus aureus isolates. J Clin Microbiol 2006;44:2481-4.  Back to cited text no. 13  [PUBMED]  [FULLTEXT]  
14.Rahbar M, Hajia M. Inducible clindamycin resistance in Staphylococcus aureus: A cross-sectional report. Pak J Biol Sci 2007;10:189-92.  Back to cited text no. 14  [PUBMED]    
15.Jenssen WD, Thakker-Varia S, Dubin DT, Weinstein MP. Prevalence of macrolides-lincosamides-streptogramin B resistance and erm gene classes among clinical strains of staphylococci and streptococci. Antimicrob Agents Chemother 1987;31:883-8.  Back to cited text no. 15  [PUBMED]  [FULLTEXT]  
16.Delialioglu N, Aslan G, Ozturk C, Baki V, Sen S, Emekdas G. Inducible clindamycin resistance in staphylococci isolated from clinical samples. Jpn J Infect Dis 2005;58:104-6.  Back to cited text no. 16  [PUBMED]  [FULLTEXT]  
17.Hamilton-Miller JM, Shah S. Patterns of phenotypic resistance to the macrolide-lincosamide-ketolide-streptogramin group of antibiotics in staphylococci. J Antimicrob Chemother 2000;46:941-9.  Back to cited text no. 17  [PUBMED]  [FULLTEXT]  
18.Huang H, Flynn NM, King JH, Monchaud C, Morita M, Cohen SH. Comparisons of community-associated methicillin-resistant Staphylococcus aureus (MRSA) and hospital-associated MSRA infections in sacramento, California. J Clin Microbiol 2006;44:2423-7.  Back to cited text no. 18  [PUBMED]  [FULLTEXT]  
19.Schreckenberger PC, Ilendo E, Ristow KL. Incidence of constitutive and inducible clindamycin resistance in Staphylococcus aureus and coagulase-negative staphylococci in a community and a tertiary care hospital. J Clin Microbiol 2004;42:2777-9.  Back to cited text no. 19  [PUBMED]  [FULLTEXT]  
20.McGehee RF, Barrett FF, Finland F. Resistance of Staphylococcus aureus to lincomycin, clindamycin, and erythromycin. Antimicrob Agents Chemother (Bethesda) 1968;8:392-7.  Back to cited text no. 20      
21.Panagea S, Perry JD, Gould FK. Should clindamycin be used in treatment of patients with infections caused by erythromycin-resistant staphylococci? J Antimicrob Chemother 1999;44:581-2.  Back to cited text no. 21  [PUBMED]  [FULLTEXT]  


    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]

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